The present invention relates to a thermal spray material that provides abrasion resistance to aluminum alloy parts. The present invention also relates to a structure that has a coating of the same. More specifically, the present invention relates to a thermal spray material that provides abrasion resistance to cylinder bores (cylinder holes), valve lifters, valve sheets, pistons, or the like. The present invention is especially effective for use inside a cylinder bore.
Thermal spraying methods that provide abrasion resistance to aluminum alloy metal parts, particularly those using inexpensive iron type material for the cylinder bore sliding surface of an internal combustion engine, have been studied for a long time. For example, in Japanese Examined Patent publication 51-10183, Japanese Examined Patent Publication 51-18004, Japanese Examined Patent Publication 54-42855, Japanese Examined Patent Publication 57-13739, and Japanese Examined Patent Publication 57-34346, there are disclosed various carbon steels that are used for aluminum cylinders. Among these, Japanese Examined Patent Publication 51-10183 and Japanese Examined Patent Publication 54-42855 aim to improve abrasion resistance by using cast iron containing a large amount of carbon (C). In Japanese Examined Patent Publication 51-18004, by including 0.3-30 weight % (in the present specification, if there is no indication to the contrary, weight % is meant) of phosphorus (P), stadite (Fe3C-Fe3P-Fe) is generated to improve abrasion resistance. However, in methods where a carbon steel coating is formed on an aluminum cylinder, there is a problem of peeling of the coating due to the heat expansion difference between the base material and the coating.
In the specification for U.S. Pat. No. 3,077,659, there is disclosed thermal spraying of a mixture of powderized aluminum and powderized iron. In Japanese Examined Patent Publication 58-54189, there is disclosed a cylinder that is thermal sprayed with a mixture of an Al Si alloy metal, containing 16-40% Si, and a high carbon ferrochrome alloy. Japanese Laid-Open Patent Publication 54-2839 discloses a thermal spray method in which, after thermal spraying with a mixture of an Al-Si alloy containing 20-40% Si, and 50% or less of carbon steel, T6 processing is conducted. Furthermore, in Japanese Laid-Open Patent Publication number 7-62519, a mixture of Al with 15% Si and 50% carbon steel (0.8% C) is thermal sprayed. The thermal spray layer is then heated to a temperature less than the melting point of the thermal spray layer.
In Japanese Laid-Open Patent Publication Number 8-253856, a piston that is thermal sprayed with a mixture of carbon steel, an Al Si alloy containing 20% or less of Si, and a carbide of Hv 500-1500 or an alloy containing a carbide, is disclosed. These thermal sprays have reduced the heat expansion difference with the base material by mixing aluminum alloy powder with iron alloys. In the last four cases, the Al Si alloy for reducing the heat expansion difference contains 15-40% Si. As a result, the heat expansion difference reducing layer also has improved abrasion resistance. However, when used for a cylinder, bore thermal spraying does not achieve an adequate thermal spray temperature for melting the thermal spray particles. With high carbon ferrochrome alloy or the usual carbon steel and cast iron, an adequate bonding between particles in the mixture thermal spray coating is not achieved. There are problems of chipping particles, abrasion, and the like.
Improvements are necessary for increasing the bonding between particles of the mixture thermal spray coating, not only with iron materials, but also with aluminum materials. In order to improve the abrasion resistance, in the invention disclosed in Japanese Laid-Open Patent Publication Number 8-253856, three types of powder are mixed, but it is difficult to distribute each of the component materials evenly within the coating. In Japanese Laid-Open Patent Publication Number 6-240436, in order to create a uniform distribution within the coating, the use of aluminum and iron based metal (such as cast iron or iron-molybdenum alloy) as a composite powder is disclosed. However, in order to make a composite powder, it is necessary that each of the powders of the aluminum and iron based metal are very fine particles. This raises the cost of the powder. Furthermore, because the reactivity of aluminum and iron based metals are high, there is the accompanying danger of a dust explosion. As a result, the handling of very fine particles by themselves should be avoided.
It is an object of the present invention to provide a thermal spray material which overcomes the aforementioned problems.
It is a further object of the present invention to provide a low cost thermal spray material that has excellent abrasion resistance and seize resistance.
It is another object of the present invention to provide a bore spraying thermal spray material that has excellent abrasion resistance and seize resistance.
It is yet another object of the present invention to provide a thermal spray material that has adequate adhesive strength to a base material at high temperatures.
It is still a further object of the present invention to provide a thermal spray material that maintains bonding strength between its particles at high temperatures.
It is another object of the present invention to provide a sliding member which has been coated with the thermal spray material of the present invention.
Briefly stated, the present invention relates to a thermal spray material which includes a mixture of 5-30 weight % of an AlSi alloy powder with 95-70 weight percent of a cast iron powder to provide abrasion resistance for aluminum alloy parts. The AlSi alloy powder contains 12-30 weight % Si, at least one element selected from a group consisting of 0.5-5.0 weight % Cu and 0.2-3.0 weight % Mg, 1-15% of at least one element selected from the group consisting of Fe, Mn, and Ni, and a mass balance of Al. The cast iron powder contains 2-4 weight % C, no more than 0.3 weight % Si, and 0.5-3.0 weight % P. A sliding surface of a sliding member is thermal sprayed with a coating of this thermal spray material to provide a sliding member having excellent abrasion resistance.
According to an embodiment of the present invention, there is provided a thermal spray material comprising a mixture of 5-30 weight % Al Si alloy powder, the alloy powder having 12-30 weight % Si, at least one element selected from the group consisting of 0.5-5.0 weight % Cu and 0.2-3.0 weight % Mg, and 1-15% of at least one element selected from the group consisting of Fe, Mn, and Ni; and 95-70 weight % of cast iron powder, the cast iron powder having 2-4 weight % C, 0.3 weight % or less Si, and 0.5-3.0 weight % P.
According to a feature of the present invention, there is provided a structure having a sliding surface of a sliding member coated with a composition comprising a mixture of 5-30 weight % Al Si alloy powder, the alloy powder having 12-30 weight % Si, at least one element selected from the group consisting of 0.5-5.0 weight % Cu and 0.2-3.0 weight % Mg, and 1-15% of at least one element selected from the group consisting of Fe, Mn, and Ni; and 95-70 weight % of cast iron powder, the cast iron powder comprising 2-4 weight % C, 0.3 weight % or less Si; and 0.5-3.0 weight % P.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.